fix: report execute hook failures

[Eilen6316]

Summary

• pass the original exception, including cancellation, to top-level execute post hooks
• defer execute hook completion for generator and async-generator APIs until iteration ends
• clear execution hook state when pre hooks or streaming setup fail
• report the correct astream_result execute method

Testing

• uv run --with pytest --with pytest-asyncio --with aiosqlite --with 'pydantic[email]>=2.0' python -m pytest tests/core --ignore=tests/core/test_graphviz_display.py -q\n- uv run --with 'opentelemetry-api' --with 'opentelemetry-sdk' --with 'langfuse>=3.0.0' --with pytest --with pytest-asyncio --with 'pydantic[email]>=2.0' python -m pytest tests/integrations/test_opentelemetry.py tests/integrations/test_burr_opentelemetry.py tests/integrations/test_burr_langfuse.py -q\n- black --check and flake8 on modified Python files